1. Field of the Invention
The present invention relates to a vehicular power supply device, particularly to a technology of operating a generator and a battery in combination with each other.
2. Description of the Related Art
There has been a technology for suppressing an inrush current generated in a power supply system, to reduce a power supply capacity and a wiring capacity. Japanese Patent Application Laid-Open 7(1995)-164982 discloses a power supply system of the technology. In the power supply system, a controlled power application prevents occurrence of a momentary overload conditions such as inrush currents at the same time. When a switch is instructed to apply power to each load, if an over-current is being supplied to the load, CPU does not supply the power to the load, and after the current is lowered to a steady current, the CPU starts supplying the power to the load.
However, once a battery as a supplementary power supply of a generator for a DC-DC converter or the like is discharged, the battery acts as a load for the generator. When a load requiring a large current, such as a lamp, is driven, large power is instantly taken out of (or discharged from) the battery, and conversely, during a subsequent charge, the large power flows into the battery. Specifically, the charge/discharge of the battery, similarly to the load such as the lamp, generates a momentary peak of the large power resulting in an increased output of the generator to the whole system.
Moreover, since a capacity of the DC-DC converter in the system depends not only on the rated current of the loads but also on the charge current for the battery as described above, the converter becomes large in size and high in cost.
The object of the present invention is to provide a vehicular power supply device being low in cost and contributing to reducing a voltage converter capacity.
A first aspect of the present invention is a vehicular power supply device, comprising: a generator generating power; a high-voltage battery being charged with power outputted from the generator, the high-voltage battery supplying the charged power to a high-voltage load; a voltage converter converting an output voltage of the high-voltage battery into another voltage; and a plurality of low-voltage batteries respectively being connected to the voltage converter in parallel and being charged with power outputted from the voltage converter, the low-voltage battery supplying the charged power to a low-voltage load.
According to the first aspect of the present invention constituted as described above, since the vehicular power supply device includes the plurality of low-voltage batteries connected in parallel for driving the load, the capacity of the respective low-voltage battery can be smaller than that of a conventional vehicular power supply device with one battery. Consequently, an inrush current during the charge of the battery and an output power capacity of the voltage converter can be reduced, thus enabling miniaturization thereof.
A second aspect of the present invention is the vehicular power supply device according to the first aspect, further comprising: a control circuit selecting at least one low-voltage battery for supplying the power required for driving the low-voltage load among the plurality of low-voltage batteries.
According to the second aspect of the present invention constituted as described above, since at least one low-voltage battery for supplying the power required for driving the load is selected, it is possible to avoid a shortage of the power when power consumption of the load exceeds the maximum output power capacity of the voltage converter due to generation of the inrush current.
A third aspect of the present invention is the vehicular power supply device according to the second aspect, in which the control circuit allows the plurality of low-voltage batteries to be sequentially charged with the power outputted from the voltage converter.
According to the third aspect of the present invention constituted as described above, since the low-voltage batteries with a smaller capacity than that of the conventional battery are sequentially charged, an amount of the inrush current can be further reduced. Consequently, the output power capacity of the voltage converter can be reduced, thus enabling miniaturization thereof.
A fourth aspect of the present invention is the vehicular power supply device according to the second aspect, further comprising: detector for detecting a charge amount of the low-voltage battery, wherein, when the power required for driving the low-voltage load is smaller than a predetermined value, the control circuit allows a low-voltage battery having a small charge amount detected by the detector to be used for supplying the power prior to the other low-voltage batteries.
According to the fourth aspect of the present invention constituted as described above, since the low-voltage battery with a larger charge amount is always maintained in a state of having the larger charge amount or of being fully charged, the low-voltage battery can be used as an auxiliary, thus avoiding a trouble due to battery depletion.
Preferably, the detector is configured with a current sensor for detecting a charge/discharge current of the low-voltage battery and a voltage sensor for detecting a voltage of a terminal thereof, the current and the voltage detected by the detector are sent to the control circuit, the control circuit calculates the charge amount based on the charge/discharge current and stores the calculated charge amount.